09 July 2012
Definition: The three dimensional, largely hidden, dense systems of urban water networks that include a potentially important network of buried headwater streams give rise to a highly connected network in which groundwater (slow) flows are interspersed with faster groundwater and surface water flows which resemble a karst hydrologic system.
Explanation: Urban landscapes offer streams (often buried in densely developed areas) and a dense surface drainage system for stormwater (e.g., gutters, swales, etc.), but these are also part of a buried, hidden water network which includes sanitary sewers, storm drains, and potable water. These interact with streams in very complex ways that result in both positive and negative water flows between the engineered, groundwater and natural stream and groundwater systems.
Example: The Baltimore stormwater drainage pipe in the headwater portion of the Watershed 263 catchment exhibits constant baseflow, even in dry weather, which is similar in magnitude to a natural forested catchment of similar drainage area.
Why Important: These complex interactions between natural and human water systems greatly increase connectivity and impact stream ecosystem structure and function in profound ways. Examples include the contributions of deicing salt to long term increasing stream chloride trends (over many decades), flows of water between streams and buried sanitary sewer interceptors (and subsequent bacterial pollution), and rising water tables because of leaking potable and sanitary sewage waters.
Contributed by BES Co-PI Kenneth T. Belt